Surface treatment of substrate or paper/paperboard products using optical brightening agent

ABSTRACT

The present invention relates to a process for applying optical brightening agent (OBA) to a sheet of paper or paperboard substrate. The process comprises the step of spraying an aqueous composition comprising an optical brightening agent onto at least one surface of a sized paperboard substrate to form a treated paperboard substrate. The treated paperboard substrate includes a layer of OBA on at least one surface of the paper or paperboard substrate in which the brightness of the treated paper or paperboard substrate is greater than the sized paper or paperboard substrate before treating thereof.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for applyingoptical brightening agent widely known as (OBA) on a paper surface by aspray coating device.

BACKGROUND OF THE INVENTION

The quality of paper or paperboard can be improved by, among other ways,treating the surface of a paper or paperboard web with a suitablechemical agent. As market demands require paper to exhibit higher levelsof brightness, optical whitener or optical brightening agent (OBA), isadded at exorbitant amounts to increase the amount of light reflectance,or brightness measured in a sheet. The OBA works by absorbing UV lightand re-emitting it at visible light wavelengths, measured in a specifiedreflective range. In these applications, the starch acts as a UV lightfilter when it is yellow colored, and prevents complete activation ofthe OBA molecule for its intended purpose of increasing brightness.

SUMMARY OF THE INVENTION

The present invention is directed to allow optical whitener orbrightener the opportunity to act as efficiently as possible when addedto a sheet of paper or paperboard. Accordingly, in present invention anOBA is applied directly to the surface of a paper by spray applicationwhich allows the OBA molecule to reside closer to the human eye (ormeasuring device) thereby permitting nothing to interfere with the lightthat is reflected back. This technique permits the OBA to act in itsmost efficient form as possible.

One aspect of the present invention reduces the amount of OBA sprayedonto the surface of the paper as compared with conventional size pressor wet end method of using mixture of starch and OBA at the size pressto obtain comparable levels of brightness through use of the presentinvention. When OBA is sprayed onto the paper surface, the human eyeaverages the area it observes and arrives at an image. Measurements havebeen made on sprayed samples and size press OBA samples and the resultscompared for measurement variability to determine if there weremeasurable fluctuations in brightness.

Another aspect of the present invention is to make immediate adjustmentsto brightness of a standard substrate at a spray nozzle instead ofwaiting for the OBA added to either the paper wet end or the size presssystem to equilibrate when OBA levels are modified. A further aspect ofthe present invention is the removal of OBA from already complex sizepress and coating formulations.

Another further aspect of the present invention relates to a process forapplying optical brightening agent (OBA) to a sheet of paper,paperboard, substrate, linerboard, and other cellulose fibers. Theprocess comprises the step of spraying an aqueous composition comprisingan optical brightening agent onto at least one surface of a paper orrelated substrate to form a treated substrate. The treated substrateincludes a layer of OBA on at least one surface of the substrate inwhich the brightness of the treated substrate is greater than thesubstrate before treating thereof.

Yet another aspect of the present invention relates to a paper orpaperboard comprising a substrate having a layer of starch being coatedthereto wherein the layer of starch including a layer of opticalbrightening agent (OBA) sprayed thereon. A layer of an aqueouscomposition comprises an optical brightening agent (OBA) being sprayedonto at least one surface of the substrate which the brightness of thetreated substrate is greater than the substrate before treating thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the invention can be gained from the followingdescription of the preferred embodiments when read in conjunction withthe accompanying drawings in which:

FIG. 1 is a portion of spray coating machine configuration according tothe present invention; and

FIG. 2 is a graphic illustration of the paper brightness variation fromthe unexposed samples with exposure time;

FIG. 3 is a graphic illustration of the result of paper brightnessvalues change as a function of exposure time;

FIG. 4 is a graphic illustration of the effect of measured fluorescenceas a function of exposure time; and

FIG. 5 is a graphic illustration of the fluorescence variation from theunexposed samples with exposure time.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible of embodiment in many differentforms, there is shown and described in drawing, figures, and examplesand will herein be described in detail preferred embodiments of theinvention with the understanding that the present disclosure is to beconsidered as an exemplification of the principles of the invention andis not intended to limit the broad aspect of the invention to theembodiments illustrated.

In the first step of the process of this invention, any cellulose fibersused to make a paper, paperboard, substrate or linerboard is treatedwith a treating composition comprising one or more optical brighteningagents (OBAs) to enhance the surface brightness of a paper. Although,paper is treated in the present invention, but any cellulose fibers suchas paper web, paperboard, substrate, and linerboard can be used in thepractice of this invention. Such paper or related webs their methods andapparatus and their manufacture are well known in the art (e.g., G. A.Smook reference book cited herein). For example, the paper or paperboardweb can be made from pulp fibers derived from hardwood trees, softwoodtrees, or alternatively, a combination of hardwood and softwood trees isprepared for use in a papermaking furnish by any known suitabledigestion, refining, and bleaching operations, as for example, knownmechanical, thermomechanical, chemical and semichemical, etc., pulpingand other well known pulping processes. In certain embodiments, at leasta portion of the pulp fibers may be provided from non-woody herbaceousplants including, but not limited to, kenaf, hemp, jute, flax, sisal, orabaca although legal restrictions and other considerations may make theutilization of hemp and other fiber sources impractical or impossible.Either bleached or unbleached pulp fiber may be utilized in the processof this invention. Recycled pulp fibers are also suitable for use. Inthe preferred embodiment, the cellulosic fibers in the paper or relatedweb include from about 0% to about 100% by weight dry basis softwoodfibers and from about 100% to about 0% by weight dry basis hardwoodfibers.

In the preferred embodiments of the invention, in addition to pulpfibers and optional additives, the paper or paperboard web also includesdispersed microspheres within the fibers and any other components ofexpanded microspheres.

Expanded and expandable microspheres are well known in the art. See forexample Expandable microspheres are described in U.S. Pat. Nos.6,802,938, 6,864,529, 3,556,934, 5,514,429, 5,125,996, 3,533,908,3,293,114, 4,483,889, and 4,133,688; and UK Patent Application 2307487,the contents of which are incorporated by reference. All suchmicrospheres can be used in the practice of this invention.

Suitable microspheres include synthetic resinous particles having agenerally spherical liquid-containing center. The resinous particles maybe made from methyl methacrylate, ethyl methacrylate,ortho-chlorostyrene, polyortho-chlorostyrene, polyvinylbenzyl chloride,acrylonitrile, vinylidene chloride, para-tert-butyl styrene, vinylacetate, butyl acrylate, styrene, methacrylic acid, vinylbenzyl chlorideand combinations of two or more of the foregoing. Preferred resinousparticles comprise a polymer containing from about 65 to about 90percent by weight vinylidene chloride, preferably from about 65 to about75 percent by weight vinylidene chloride, and from about 35 to about 10percent by weight acrylonitrile, preferably from about 25 to about 35percent by weight acrylonitrile.

The amount of microspheres may vary widely and depends on the desiredexpanded microsphere volume in the final paper product. Preferably thepaper includes from about 0.5 to about 5.0 wt % expanded microspheresand more preferably from about 1.0 to about 2.0 wt % by dry weight ofthe paper or paperboard web.

The paper may include conventional additives such as, for example,starch, mineral fillers, sizing agents, retention aids, andstrengthening polymers. Among the fillers that may be used are organicand inorganic pigments such as, by way of example, polymeric particlessuch as polystyrene latexes and polymethylmethacrylate, and mineralssuch as calcium carbonate, kaolin, and talc. Other conventionaladditives include, but are not restricted to, wet strength resins,internal sizes, dry strength resins, alum, fillers, pigments and dyes.For obtaining the highest levels of surface sizing in the processes ofthis invention, it is preferred that the sheet is internally sized,which means, sizing agents be added to the pulp suspension before it isconverted to a paper sheet. Internal sizing helps prevent the surfaceand sprayed OBA from soaking into the sheet, thus allowing it to remainon the surface where it has maximum effectiveness. The internal sizingagents encompass any of those commonly used at the wet end of a finepaper machine. These include rosin sizes, ketene dimers and multimers,and alkenylsuccinic anhydrides. The internal sizes are generally used atlevels of from about 0.05 wt. % to about 0.25 wt. % based on the weightof the dry paper sheet. Methods and materials utilized for internalsizing with rosin are discussed by E. Strazdins in The Sizing of Paper,Second Edition, edited by W. F. Reynolds, Tappi Press, 1989, pages 1-33.Suitable ketene dimers for internal sizing are disclosed in U.S. Pat.No. 4,279,794, which is incorporated by reference in its entirety, andin United Kingdom Patent Nos. 786,543; 903,416; 1,373,788 and 1,533,434,and in European Patent Application Publication No. 0666368 A3. Ketenedimers are commercially available, as Aquapel.RTM and Precis.RTM sizingagents from Hercules Incorporated, Wilmington, Del. Ketene multimers foruse in internal sizes are described in: European Patent ApplicationPublication No. 0629741A1, corresponding to U.S. patent application Ser.No. 08/254,813, filed Jun. 6, 1994; European Patent ApplicationPublication No. 0666368A3, corresponding to U.S. patent application Ser.No. 08/192,570, filed Feb. 7, 1994; and U.S. patent application Ser. No.08/601,113, filed Feb. 16, 1996. Alkenylsuccinic anhydrides for internalsizing are disclosed in U.S. Pat. No. 4,040,900, which is incorporatedherein by reference in its entirety, and by C. E. Farley and R. B.Wasser in The Sizing of Paper, Second Edition, edited by W. F. Reynolds,Tappi Press, 1989, pages 51-62. A variety of alkenylsuccinic anhydridesare commercially available from Albemarle Corporation, Baton Rouge, La.

The density, basis weight and caliper of the paperboard web of thisinvention may vary widely and conventional basis weights, densities andcalipers may be employed depending on the paper-based product formedfrom the web. Paper or paperboard of invention preferably have a finalcaliper, after calendering of the paper, and any nipping or pressingsuch as may be associated with subsequent coating of from about 2 milsto about 30 mils although the caliper can be outside of this range ifdesired. More preferably the caliper is from about 4 mils to about 20mils, and most preferably from about 7 mils to about 17 mils.

Paper or paperboard substrate of the invention preferably exhibits basisweights of from about 17 lb/3000 ft² to about 300 lb/3000 ft², althoughpaper or paperboard substrate basis weight can be outside of this rangeif desired. More preferably, the basis weight is from about 10 lb/3000ft² to about 200 lb/3000 ft², and most preferably from about 35 lb/3000ft² to about 150 lb/3000 ft².

The final density of the paper or paperboard, which is defined as thebasis weight divided by the caliper, is preferably from about 6 lb/3000ft²/mil to about 14 lb/3000 ft²/mil although paper or paperboarddensities can be outside of this range if desired. More preferably, thepaper or paperboard density is from about 7 lb/3000 ft²/mil to about 13lb/3000 ft²/mil and most preferably from about 9 lb/3000 ft²/mil toabout 12 lb/3000 ft²/mil.

The paper or paperboard substrate has moisture content of at least 3%and no more than 60%. While I do not wish to be bound by any theory, itis believed that the moisture content is 35%. The moisture content ispreferably 30%, more preferably 25% and most preferably 22%.

Substrates employed in the invention are not critical and any cellulosefibers such as paper, paper web, paperboard, and linerboard can be usedin the practice of this invention. Useful substrates include a varietyof coated and uncoated paper, paperboard and related products, includingbleached or unbleached, hardwood or softwood, virgin or recycled, andall coated and uncoated forms of paper made from a variety of chemical,semi-chemical and mechanical pulps such as wood, Kraft, ThermoMechanical Pulping (TMP), ChemiThermoMechanical Pulping (CTMP), BleachedChemical Thermomechanical Pulp (BCTMP), and Ground Wood (GW).

Optical brightening agents (“OBAs”) used in the practice of the processof this invention may vary widely and any conventional OBA used or whichcan be used to brighten mechanical or Kraft pulp can be used in theconduct of the process of this invention. Optical brighteners aredye-like fluorescent compounds are substances that absorb light in theinvisible ultraviolet region of the spectrum and reemit it in thevisible portion of the spectrum, particularly in the blue to blue violetwavelengths. This provides added brightness and can offset the naturalyellow cast of a substrate such as paper. Optical brighteners used inthe present invention may vary widely and any suitable opticalbrightener may be used. An overview of such brighteners is to be found,for example, in Ullmann's Encyclopedia of Industrial Chemistry, SixthEdition, 2000 Electronic Release, OPTICAL BRIGHTENERS—Chemistry ofTechnical Products which is hereby incorporated, in its entirety, hereinby reference. Other useful optical brighteners are described in U.S.Pat. Nos. 5,902,454; 6,723,846; 6,890,454; 5,482,514; 6,893,473;6,723,846; 6,890,454; 6,426,382; 4,169,810; and 5,902,454 and referencescited therein which are all incorporated by reference. Still otheruseful optical brighteners are described in; and U.S. Pat. ApplicationPublication Nos. US 2004/014910 and US 2003/0013628; and WO 96/00221 andreferences cited therein which are all incorporated by reference.Illustrative of useful optical brighteners are4,4′-bis-(triazinylamino)-stilbene-2,2′-disulfonic acids,4,4′-bis-(triazol-2-yl)stilbene-2,2′-disulfonic acids,4,4′-dibenzofuranyl-biphenyls, 4,4′-(diphenyl)-stilbenes,4,4′-distyryl-biphenyls, 4-phenyl-4′-benzoxazolyl-stilbenes,stilbenyl-naphthotriazoles, 4-styryl-stilbenes, bis-(benzoxazol-2-yl)derivatives, bis-(benzimidazol-2-yl) derivatives, coumarins,pyrazolines, naphthalimides, triazinyl-pyrenes, 2-styryl-benzoxazole or-naphthoxazoles, benzimidazole-benzofurans or oxanilides.

Most commercially available optical brightening agents are based onstilbene, coumarin and pyrazoline chemistries and these are preferredfor use in the practice of this invention. More preferred opticalbrighteners for use in the practice of this invention are opticalbrighteners typically used in the paper industry based on stilbenechemistry such as 1,3,5-triazinyl derivatives of4,4′-diaminostilbene-2,2′-disulfonic acid and salts thereof, which maycarry additional sulfo groups, as for example at the 2, 4 and/or 6positions. Most preferred are the commercially available stilbenederivatives as for example those commercially available from Ciba Geigyunder the tradename “Tinopal”, from Clariant under the tradename“Leucophor”, from Lanxess under the tradename “Blankophor”, from 3Vunder the tradename “Optiblanc” such as disulfonate, tetrasulfonate andhexasulfonate stilbene based optical brightening agents. Of these mostpreferred commercial optical brightening agents, the commerciallyavailable disulfonate and tetra sulfonate stilbene based opticalbrightening agents are more preferred and the commercially availabledisulfonate stilbene based optical brightening agents is most preferred.

The amount of optical brightener used in the practice of the process ofthis invention can vary widely and any amount sufficient to provide thedesired degree of brightness can be used. In general, the lesser theamount of optical brightener employed the less the enhancement in TAPPIbrightness of the final pulp product. Conversely, the greater the amountof optical brightener used the greater the enhancement in pulpbrightness except that while we do not wish to be bound by any theory,it is believe that at some point the addition of more optical brightenerwill not have any further appreciable impact on pulp brightness and mayeven result in a decrease in pulp brightness. The amount of opticalbrightener used is usually at least about 1 wgt % based on tons of paperproduced. Preferably the amount of optical brightener is from about 0.5to about 2 wgt %, more preferably from about 0.75 to about 1.75 wgt %and most preferably from about 1 to about 1.5 wgt % on theaforementioned basis.

The amount of the OBA in the aqueous solution can be varied widely andany amount can be used. For example, the amount of OBA can be as high as50%. The amount of OBA is preferably 25%. More preferably, the amount ofOBA in the aqueous solution is from 2-10%. Most preferably, the amountof OBA in the aqueous solution is from 5-10%. It was determined that 2%concentration of OBA is optimum for visual purposes. Subsequent trialsmodifying optical properties have used higher concentrations of appliedchemical. This can be dependent or independent of machine speed. The OBAapplication weight is generally, but not limited to, 0.7 wt %. Morepreferably, the application weight of OBA is 1.1 wt %. Most preferably,the basis weight of OBA is 0.9 wt %. The OBA is predominately at or neara surface of the paper or paperboard substrate. For example, the amountof OBA at the surface of the paper or paperboard substrate can greaterthan 90%.

The aqueous composition may also include various optional components.These components include, but not limited to color bodies or surfaceproperties.

The physical characteristics and properties of these commerciallyavailable materials are non-abrasive, non-agglomerating, water solubleand tack free and further described in technical data sheets which areincorporated herein by reference. These include, but are not limited to,dyes, OBA, charge polymers, inorganic salts and surface sizing.

The layer or coating can be applied to the paper using conventionalspray fluid application apparatuses. Such apparatuses are noncontactingequipment that is well-known and frequently used in the art of paintingand fluid application systems technology. For example, high-pressurespraying equipments with suitable nozzles are commercially available forfinishing or coating a surface. These apparatuses are described indetail in SPRAYING SYSTEMS COMPANY.

The paper, paperboard, substrate or linerboard manufactured inaccordance with this invention can be used for conventional purposes.For example, the paper is useful as publication paper, packaging and thelike. The paper includes a base layer, a starch layer, and an OBA layersprayed on the starch layer. The paper exhibits superior TAPPIbrightness as determined by procedure of T452 OM-98 when compared to thepaper used OBA before the size press. The TAPPI brightness of the paperis preferably at least about 75, more preferably from about 84 to about92 and most preferably from about 92 to about 96.

FIG. 1 depicts a portion of spray coating machine configuration used inthe process of applying OBA to a sheet of paper in accordance to thepresent invention. The apparatus 10 comprises a mixing chamber 12, atleast one nozzle 14, and a pair of tubes 16 and 18. The nozzle 14 andthe pair of tubes 16 and 18 are attached to the mixing chamber 12 sothat the aqueous composition 19 can be delivered onto the surface of thepaper 20. Each of the tubes 16 and 18 are connected to a respectivestorage tank (not shown). Tube 16 transfers aqueous composition 19generally, at atmospheric pressure, from the storage tank to the mixingchamber 12. On the other hand, tube 18 transfers compressed air, aboveatmospheric pressure, to the mixing chamber 12 for atomizing the aqueouscomposition 19. In the commercial applications, it is preferable toattach multiple spray nozzles to the mixing chamber 12 so that theentire width of the paper 20 can be sprayed with the aqueous composition19. The function of the nozzle 14 or alternatively, the multiple spraynozzles, is to atomize the ejected aqueous composition 19 jet into anaerosol and then to direct this aerosol to the surface of the paperbeing coated. Hence, the nozzle must be capable of spraying the aqueoussolution in a homogeneous and all-covering manner in order to achieve ahigh-quality and homogeneous layer of the applied coat. The pressurizedaqueous composition 19 is fed into the spray nozzle 14 via a separateduct, and the atomization of the aqueous composition is performed withthe help of compressed air passed to the nozzle.

The air atomization of the aqueous composition is preferred becausemicro particles cover the surface of the paper and allow the human eyeto “average” the viewing area and judge the appearance. These microparticles are very small droplets that cover the majority of the surfaceand make the human eye perceive the majority of the surface aspossessing the desired characteristics. Atomization also requires lessactive agent for comparable results than conventional surface or wet endapplications. Also, atomization requires less water to carry aqueouscomposition onto the paper, and therefore needs less energy to dry theapplied layer.

To produce an atomized particle, a collision of air and aqueous solutionmust happen under controlled circumstances. There were several type ofair nozzles experimented with to determine an optimum atomization withlower liquid flow rates and sufficient air pressure for dropletdistribution and paper coverage. The two types of spray nozzles used forthe present invention are internal and external mixing. The internalmixing nozzle allows the collision to occur inside the apparatus, butthe external nozzle collide the air and aqueous solution outside thespray nozzle body. The external nozzle uses higher liquid flows toovercome extraneous forces, and reduces the efficiency of the targetedgoal. Although the internal mixing is preferred for the presentinvention, the external mixing may be used as well.

The fluid delivery can be varied widely in the present invention. Forexample, the fluid delivery is from 1.4 to 8.4 gallons per hour pernozzle for the development of the apparatus used in the presentinvention. More preferably, the fluid delivery is from 2.4 to 6.3gallons per hour per nozzle depending on the OBA concentration. Mostpreferably, the fluid delivery for the nozzle efficiency was a nozzledelivering approximately 4.1 gallons per hour. These operationalconditions enhanced the brightness value and provided the maximumspraying coverage of the sheet of paper.

Air pressure can be varied widely in the present invention. Tosufficiently atomize the aqueous solution, the air pressure is fromabout 20 psi to about 60 psi. More preferably, the air pressure toatomize the aqueous solution is from about 30 psi to about 50 psi. Mostpreferably, the air pressure to atomize the aqueous solution is fromabout 40 psi to about 45 psi.

Concentration of OBA can be varied widely. Different dilutions of theaqueous solution may be delivered onto the sheet of paper. Becauseatomization is such an efficient process for applying OBA to the sheetof paper, very low concentrations of aqueous solution can be used. Thedilution rate is ranged from about 1% to about 5% concentration of OBA,diluted in deionized water. More preferably, the dilution rate is rangedfrom about 2.5% to about 5% concentration of OBA. Most preferably, thedilution is rate ranged from about 3.5% to about 5% concentration ofOBA. Depending of coverage area of the sheet of paper and the speed ofthe paper machine, this may be manipulated.

According to the present invention, an air atomization spray nozzle(Spraying Systems Co. PN 73320.flat) was used to apply a 2% dilutesolution of Clariant BCW hexasulfonated optical whitener (mixed withwater) to a moving web using compressed air to deliver 4 gallons perhour of the liquid to the nozzle. More preferably, an air atomizationspray nozzle was used to apply a 5% dilute solution of Clariant BCWhexasulfonated optical whitener (mixed with water) to a moving web. Mostpreferably, an air atomization spray nozzle was used to apply a 2%dilute solution of Clariant BCW hexasulfonated optical whitener (mixedwith water) to a moving web. The internal mix atomization nozzle uses 40psi air pressure to cause the sufficient atomization of the solution andadequate coverage of the web. Multiple spray nozzles may be used to setover a larger width web to allow complete web coverage. For thisapplication, the apparatus is mounted right after the size press andapply the spray solution of OBA to the wet web just prior to enteringthe dryer. If both sides of the web are to be sprayed, an upper andlower boom may be installed on a paper machine. The dilution of thesolution can be modified to assist with sufficient coverage of the webin terms of water addition versus brightness gain. In a mill-typesituation, ultra-filtered water and OBA would need to be used to reducepotential plugging of the spray nozzle orifice.

The following specific examples are intended to illustrate the inventionin detail and are not intended to be construed as a limitation thereon.

EXAMPLE

A 74 lb basis weight, envelope grade non-fluorescent containing paperweb was placed onto the unwind stand of the size press in the papermachine. The paper was fed through the paper machine as typical andwound up on the core at the end of the paper machine. An ethylatedstarch batch was cooked to 16 percent solids which was diluted to 14percent in preparation for application onto the paper web. The starchwas fed into a puddle pilot size press and the paper web run through theoperation to allow all portions of the system to equilibrate. After afew minutes, a 36″ by 12″ piece of paper web was taken from the papermachine and measured for starch pickup, which was approximately 100pounds per ton. After target pickup of starch was verified, anatomization spraying nozzle (made by SPRAYING SYSTEMS COMPANY) wasplaced above the moving paper web and a 2% solution of a hexasulfonatedstilbene based OBA obtained from CLORIANT Corporation under the Tradename BCW was sprayed on the paper web. The OBA solution was deliveredwith a canister using pressurized air to leverage displacement of thefluid to the nozzle. By controlling the air pressure to 40 psi, thevolume of flow could be controlled to optimum delivery rates. In someexperiments, hexasulfonated stilbene OBA was then added to the starchbatch after spraying OBA onto a moving paper web surface with wet starchas a comparison data point,. The spray nozzle was turned off, and then a4 percent amount of hexasulfonated stilbene OBA, as received, was addedto the starch batch, based on weight. Once the starch application systemwith OBA was equilibrated, another sample was taken of the paper web andmeasured to verify target starch pickup of approximately 100 psi. Thisprocedure of adding 4 percent OBA was done as a control to mimic typicalOBA application in a paper mill. One final trial parameter was examinedwhere both conditions of OBA was applied in the starch, as typical, aswell as OBA sprayed onto the surface. The Tappi brightness of the sheetswas measured using the procedure of TAPPI T452 OM-98. Process parametersand the results of the Tappi brightness evaluations are set for the inthe following Table I.

TABLE I Internal Mix Atomization Spray Nozzle - No. 73320.flat I1 I2 I5Size press OBA in I3 I4 OBA in I6 Starch Starch Spray Parameters SprayGeneral Run # Applied Content Air (psi) Fluid (psi) Content Comments 0no — — — None Base control w/o heat 1 no — — — None Base control w/ heat2 yes None — — None Base control w/ starch only 3 yes None 12 10 2%Hexasulfonated 2.17 gph/side spray 4 yes None 20 20 2% Hexasulfonated3.35 gph/side spray 5 yes None 42 40 2% Hexasulfonated 4.14 gph/side 6yes None 65 50 2% Hexasulfonated 3.02 gph/side spray 7 yes 4%Hexasulfonated — — None OBA control 8 yes 4% Hexasulfonated 12 10 2%Hexasulfonated 2.17 gph/side spray 9 yes 4% Hexasulfonated 20 20 2%Hexasulfonated 3.35 gph/side spray 10  yes 4% Hexasulfonated 42 40 2%Hexasulfonated 4.14 gph/side spray 11  yes 4% Hexasulfonated 65 50 2%Hexasulfonated 3.02 gph/side spray I14 I7 I12 Brightness unit Size pressI9 Avg. TAPPI I13 gain per Run # OBA (#/T) Spray OBA (#/T) BrightnessBrightness Gain OBA pound 0 — — 78.9 — 1 — — 78.9 0 — 2 0.0 0.0 77.9 −10.000 3 0.0 14.3 80.4 1.5 0.105 4 0.0 22.1 82.6 3.7 0.167 5 0.0 27.382.8 3.9 0.143 6 0.0 19.9 82.2 3.3 0.166 7 38.4 0.0 83.1 4.2 0.109 838.4 14.3 83.7 4.8 0.091 9 38.4 22.1 83.6 4.7 0.078 10  38.4 27.3 83.64.7 0.071 11  38.4 19.9 83.8 4.9 0.084

Table I has numeric labels for the runs and alpha-numeric labels foreach parameter and test condition. Starting with the runs, labeled 0through 11 on the internal and 12 through 17 on the external mix spraynozzles, each number specifies a run condition. Run number 0 is theprimary control; no heat, no starch, and no OBA applied to the sheet,either sprayed or with starch as a carrier. Run number 1 is a secondarycontrol where the just the paper was run through the machine dryingsystem with no starch and no OBA applied. Run number 2 is a basiccontrol where only starch is applied to the web along with heat to dryit. This is used as the baseline for comparison to determine how muchbrightness can be built on the sheet with OBA applied; either sprayedwith both types; internal and external mix, and added into the starch.The internal mix spray apparatus (top chart) had better coverage withlower flow rates, so it will be referenced for the remainder of thistext. Runs 3 through 6 all had OBA applied via spray to the surface ofthe sheet, but had no OBA mixed in the starch solution. The variablewithin these runs was the amount of OBA-containing spray applied to thesurface. Column 16 shows the spray flow amounts of a 2% solution of OBAand water, used as a carrier. For the spray nozzle to work properly, airand fluid flow pressure has to be monitored and properly delivered tothe spray head to efficiently cover the web. These parameters areidentified in columns 13 and 14.

Overall, these series of runs were to determine at what point sprayapplication fluorescence would compare to a typical OBA-mix starchsolution. This can be calculated by measuring the sheet containingoptical whitener for brightness and comparing to the sheet with onlystarch. Run number 7 (highlighted), was used as standard for comparisonbecause it is the typical application amount of OBA in starch at papermills. Looking at comparable brightness builds, run number 5 (alsohighlighted) was the closest in brightness builds. When calculations aremade for the amount of OBA applied in each method to gain comparablebrightness, column I11 shows the spray application method exhibits asignificant savings over traditional size press (starch containing)application methods for comparable brightness gains.

The several paper samples of runs in Table I were evaluated for fade.Fading of the paper typically results in loss of brightness and/orfluorescence, as well as color change. The test samples were; a controlof the paper with no starch (A), a sample of the paper with only starch,no OBA (2), the optimum spray condition previously discussed (5), thetypical OBA addition in starch, also mentioned previously (7). Alsoadded to the testing was a combination of spray and starch appliedoptical whitener, for investigation purposes (10). Two commercialproduction sheets, sample P1 and P2 were evaluated for comparisonpurpose in the Table II.

The initial sheet brightness for all test sheets is approximately 84.The sheets were irradiated at 1.0 watt/m²@420 nm with xenon light sourcesimulating indoor light for 0, 2, 4, 7 and 10 hours inside an ATLASweatherometer and tested for TAPPI brightness and fluorescence. Thehumidity and the temperature for the test are 45% and 30 C. The resultsare set forth in Table II and in FIGS. 2, 3, 4 and 5.

TABLE II Internal Mix Nozzle 73320.flat W1 W2 W5 Size press OBA in W3 W4OBA in W6 Starch Starch Spray Parameters Spray General Run # AppliedContent Air (psi) Fluid (psi) Content Comments A no — — — None Sheet w/no starch, no OBA 2 yes None — — None Sheet w/ starch, no OBA 5 yes None42 40 2% Hexasulfonated Sheet w/ starch, spray OBA 7 yes 4%Hexasulfonated — — no Sheet w/ starch, size press OBA 10  yes 4%Hexasulfonated 42 40 2% Hexasulfonated Sheet w/ starch, size press &spray OBA P1 — — — — — Typical Production Control (84 Bright) P2 — — — —— Typical Production Control (84 Bright) W7 W8 W9 W10 W11 W13 W14 W15W16 W17 Exposure time (hours) vs. Exposure time (hours) vs. TAPPIBrightness measurement Fluorescence measurement Run # 0 2 4 7 10 0 2 4 710 A 78.9 79.2 79.3 79.8 79.6 0 0 0 0 0 2 77.9 78.2 78.5 78.7 79.3 0 0 00 0 5 82.7 82.8 83.2 83.2 82.8 5.0 5.5 5.2 4.9 4.7 7 83.4 83.2 83.1 83.082.9 5.6 5.1 4.9 4.7 4.4 10  84.3 83.8 83.5 83.6 83.4 6.9 6.5 6.2 6.05.8 P1 84.0 83.3 83.5 83.7 83.6 2.6 2.3 2.2 2.2 2.0 P2 83.5 82.3 82.282.3 82.6 2.3 2.1 1.9 1.8 1.7 Samples tested in an ATLAS 3000i+weatherometer under sunlight through window pane simulated conditions.TAPPI Brightness and Fluorescence values measuerod on a Technidyne S-4Mbrightness meter.

As shown in Table II, all test samples are labeled by run number andtest condition for illustration purposes. FIG. 2 shows the result ofsheet brightness versus exposure time. FIG. 4 plots the change from theunexposed control against time. FIG. 3 shows the effect on measuredfluorescence versus time. FIG. 5 shows the variation from the unexposedsamples with exposure time. FIGS. 2 and 3 show the testing results offade on TAPPI brightness. FIGS. 4 and 5 the fade results onfluorescence. In FIG. 1 each test parameter shows the absolute valuesand the following chart display the change from the non exposed sample.All values in the FIG. 2 are plotted against exposure time.

Various modifications and variations may be devised given theabove-described embodiments of the invention. It is intended that allembodiments and modifications and variations thereof be included withinthe scope of the invention as it is defined in the following claims.

1. A process for applying optical brightening agent to a sized paper orpaperboard substrate, the process comprising: spraying an aqueouscomposition comprising an optical brightening agent (OBA) onto at leastone surface of the sized paper or paperboard substrate having a surfaceTAPPI brightness of (x) to form a treated sized paper or paperboardsubstrate having a layer of OBA on the at least one surface of the sizedpaper or paperboard substrate having a surface TAPPI brightness of (y),wherein (y) is greater than (x).
 2. The process of claim 1 wherein thetreated paper or paperboard substrate consists of a layer of base stock,a layer of starch sizing on a surface of the base stock, and the layerof OBA.
 3. The process of claim 1 wherein the aqueous compositioncomprises less than about 2 wt % of OBA based on the total weight of theaqueous composition.
 4. The process of claim 1 wherein the opticalbrightening agent on the surface of the treated sized paper or substrateis in amount from about 0.1 wt % to about 2 wt % per ton of total weightof paper or paperboard substrate.
 5. The process of claim 1 wherein theaqueous composition is sprayed using a plurality of spray nozzlesarrayed to extend across a width of the sized paper or paperboardsubstrate.
 6. The process of claim 5 wherein a distance between thespraying nozzle and the paper or paperboard substrate is from 10 mm to200 mm.
 7. The process of claim 1 wherein the aqueous composition isatomized.
 8. The process of claim 7 wherein the aqueous composition isatomized by mixing with a stream of air under pressure before beingapplied onto the surface of the paper or paperboard substrate.
 9. Theprocess of claim 8 wherein the pressure of air ranges from about 10 psito about 60 psi process.
 10. The process of claim 1 wherein the aqueouscomposition supplied to the spraying nozzles at pressure from about 10psi to about 60 psi.
 11. The process of claim 1 wherein the paperboardsubstrate is lightweight base stock in range of about 10 lbs/3300 ft² toabout 300 lbs/3300 ft².
 12. The process of claim 1 wherein the sprayingcomprises steps of introducing the aqueous composition into a mixingchamber having multiple spray nozzles thereon and wherein the mixingchamber configured to be extending across a width of the moving paper orpaperboard substrate; and dispersing the aqueous composition from themixing chamber onto the one surface of the moving paper or paperboardsubstrate wherein the mixing chamber is positioned proximate the onesurface of the moving paper or paperboard substrate.
 13. The process ofclaim 1 wherein the OBA is applied to the paperboard substrate after thesize press and before the reel operation.
 14. The process of claim 1wherein the OBA is applied to the moving sized paperboard substrate inamount of about 15 lbs of OBA per ton of paperboard.
 15. The process ofclaim 1 wherein the treated surface of the paperboard substrate with theOBA after the size press reduces the usage of OBA by at least 30% whilemaintaining or improving optical properties of the web of the paper. 16.A paper or paperboard comprising: a substrate comprising pulp fibers; alayer of starch coated onto a surface of the substrate; and a layercomprising an optical brightening agent (OBA) sprayed onto at least onesurface of the layer of starch.
 17. A paper or paperboard comprising: asubstrate comprising pulp fibers and an optical brightening agentwherein the optical brightening agent is predominately at or near asurface of the substrate.